564 DISEASES/DISORDERS
CLINICAL FEATURES
Single or multiple discrete subcutaneous nodules or draining tracts; more often mul-
tiple in dogs (Figures 38.1, 38.2).
Dogs (SNP): primarily dorsal trunk and neck.
Cats (panniculitis): primarily ventral abdomen and ventrolateral thorax; most often
single nodule.
Early cases of single or multifocal disease: nodules are freely movable underneath the
skin; skin overlying the nodule is usually normal but may become erythematous or
purpuric (Figure 38.3).Nodules may become cystic, ulcerate, and develop draining tracts (Figures 38.4,
38.5).
Often painful before and just after rupturing.
Ulcerations heal with crusting and scarring (Figures 38.6, 38.7).
Nodules vary from a few millimeters to several centimeters in diameter; may be firm
and well circumscribed or soft and poorly defined; may affix to the deep dermis with
enlargement (Figure 38.8).Involved fat may necrose.
Exudate: small amount of oily discharge; yellow-brown to bloody.
Multiple lesions (dogs and cats): systemic signs common (e.g., anorexia, pyrexia,
lethargy, and depression).
Occasionally associated with arthropathies in dogs.
DIFFERENTIAL DIAGNOSIS
Deep Pyoderma
More common than panniculitis.
More likely over pressure points, often more generalized.
May have associated superficial pyoderma (e.g., papules, pustules, and epidermal
collarettes).
Aspirates and impression smears: marked numbers of neutrophils with variable num-
bers of mononuclear cells and bacteria; culture/sensitivity and biopsies: confirm
diagnosis.Cutaneous Cysts
Usually nonpainful.
Well demarcated and usually not characterized as “melting,” as is often noted with
panniculitis.
Minimal inflammation.
Aspirates: amorphous debris; no inflammatory cells, not characterized as fat necrosis
but rather a thick sebaceous secretion.
Biopsies: confirm diagnosis.